DIFFERING EFFECTS OF ACID VERSUS NEUTRAL PHOSPHATE THERAPY OF HYPERCALCIURIA

Studies were performed on 12 patients with idiopathic hypercalciuria to evaluate the hypothesis that the acid load accompanying potassium acid phosphate would adversely affect renal calcium reabsorption and citrate excretion compared to the neutral form of the phosphate salt. During acute clearance studies, neutral phosphate (NP) led to a fall in FECa (2.2 ± 0.6% to 0.8 ± 0.1%, P < 0.02) and no change in titratable acidity (TA) or net acid excretion (NAE). Acid phosphate (AP) did not reduce FECa acutely, and led to a rise in TA (22 ± 4 to 62 ± 6 μEq/min, P < 0.02) and NAE (46 ± 6 to 89 ± 7 μEq/min, P < 0.02). During chronic administration, AP resulted in higher urinary calcium excretion in both absorptive (187 ± 29 vs. 141 ± 18 mg/day, P < 0.02) and renal hypercalciuric patients (233 ± 24 vs. 173 ± 190.02 mg/day, P < 0.02). Also, TA and NAE were higher following AP, whereas citrate excretion was lower (375.4 ± 64.6 vs. 633.4 ± 28.8 mg/day, P < 0.01). These data suggest that the reported ineffectiveness of AP in the therapy of nephrolithiasis may be related to the deleterious effects of the acid load on calcium and citrate metabolism.